Nucleoside analogue reverse transcriptase inhibitors (NRTIs) have been developed as drugs against human immunodeficiency virus type 1 (hereinafter referred to as “HIV-1”) and currently used as major therapeutic HIV drugs. Nevertheless, a prototype thereof, i.e., zidovudine (AZT), is known to inhibit not only reverse transcription of viruses but also DNA replication of normal cells (see, Non Patent Literature 1). Various types of Nucleoside analogue reverse transcriptase inhibitors are also known to have an antiviral effect against human T-cell leukemia virus type 1 (hereinafter referred to as “HTLV-1”), which is a human retrovirus similar to HIV-1. Further, combination therapy with interferon (IFN) and zidovudine has been known as effective for adult T-cell leukemia (hereinafter referred to as “ATL”) caused by HTLV-1 infection (see Non Patent Literatures 2 and 3). However, zidovudine is reported to have no anti-cancer effect against ATL cells in vitro (see Non Patent Literature 4) and thus mechanism of action of zidovudine on ATL cells remains poorly understood.
One of NRTIs, abacavir (ABC), is clinically used as an anti-HIV drug and also reported to have an anti-HTLV-1 effect (see Non Patent Literature 5). However, abacavir is not known to have an anti-cancer effect.